We investigated effects of atherosclerosis on mechanical distensibility characteristics of the aorta in the KHC rabbit at 10-12 months of age in relation to alteration in histological fine architecture and compared with those in the normal rabbit of the same age range. Circumferential strips of the aortic wall at 3 mm in width were sampled from the ascending, proximal and middle thoracic, and proximal and distal abdominal aortas for tension-strain and stress-strain tests and from the ascending, proximal thoracic and proximal abdominal aortas for stress-relaxation test. The strips were mounted into especially-designed chucks of a chamber fixed to tensile testing instruments, immersed into the Ringer's solution at 37℃ and sretched at a speed of 4.17 mm⁄sec by indicating tension at 20-40 g for tension-strain and stress-strain tests and at a speed of 83.33 mm⁄sec by 50% to the initial length for stress-relaxation test.The strips were kept stretched for 5 min to measure relaxation strength 5 min after the stretching for the latter test. The aortic wall in the KHC rabbit showed marked viscoelastic properties, e.g. a significant decrease in wall stress and elastic modulus, and a significant increase in relaxation strength in comparison to those in the normal rabbit, above all, in the ascending, proximal thoracic and proximal abdominal aortas in which atheromatous plaque with abundant cholesterol-rich foam cells was observed. In addition to the viscoelastic properties, a decrease in distensibility, e.g. a significant increase in wall tension was observed in the ascending aorta, which is partly due to proliferation of the collagen fibers. We can conclude that mechanical distensibility characteristics of the aortic wall reflect severity of alteration in the wall architecture due to atherosclerosis.
